1. Field of the Invention
The present invention relates generally to a device and method for temperature measurement of a liquid contained in a pressurizer vessel of a nuclear power plant and, more particularly, to such a device and method which measure the temperature of the liquid at preselected elevations for detecting temperature gradients in the liquid.
2. Description of the Related Art
A typical nuclear power facility includes a nuclear reactor wherein a controlled nuclear reaction, which generates heat, is occurring. Typically, borated water is contained in the reactor for controlling the nuclear reaction process and for passing the heat away from the reactor. A primary loop communicating with the reactor functions to pass the borated water (i.e., the heat) away from the reactor and to transfer the heat to a secondary loop. The secondary loop is isolated from the primary loop and generates steam from the heat passed from the primary loop. The steam of the secondary loop is used to produce electricity as is well known in the art. The primary loop then returns the borated water back into the reactor where the above described process is repeated.
A pressurizer vessel is connected to the primary loop for maintaining a constant pressure in the primary loop. The pressurizer vessel includes a protective shell forming an interior portion for containing any water and steam therein. The protective shell includes a cylindrical shaped side terminating at a hemispherical shaped head at both its top and bottom end, with the bottom end attached to a cylindrical support skirt. An outwardly extending flange extends radially outwardly from the skirt bottom for attaching it to its support structure, typically a floor. A nozzle at the bottom of the lower hemisphere connects to piping which attaches to the primary loop for allowing the primary loop and the pressurizer vessel to pass the borated therebetween which, in turn, functions to maintain proper pressurization of the primary loop. A heater support plate is located in a lower portion of the shell interior for receiving a plurality of electrical heaters which, during plant operation, are turned on to further heat the water or to maintain the temperature of the water at a constant temperature. A spray valve is positioned at an upper portion of the shell interior for spraying water in the shell interior which condenses the steam back to water. A liquid space temperature detector is attached to the shell side and projects radially into the interior of the shell for measuring the water temperature.
During operation of the power plant, a transient event that could decrease system pressure, for example, is counteracted by increasing the water temperature via the electrical heaters which, in turn, causes a portion of the water to flash to steam. An increasing pressure transient is limited by spraying cooler water from the primary loop via the spray valve into the shell interior which, in turn, causes a portion of the steam to condense to water.
The detector is positioned below and generally parallel to the water surface so that the temperature of the water is detected at a constant elevation. However, the water level varies up and down in the vessel interior during operation due to the electrical power demand of the power plant; thus, the temperature detector monitors different portions of the water as it varies up and down in the vessel interior. If a vertically oriented, temperature gradient exists, as is usually the case, it will only be detected when it passes upwardly or downwardly past the temperature detector.
Although the present device for monitoring the water temperature is satisfactory, it is not without drawbacks. The water temperature is presently measured at only one elevation so that temperature gradients are only detected when the water level rises or falls enough to cause the temperature gradient to pass by the temperature detector. Therefore, temperature gradients are not detected on a real time basis.
Consequently, a need exists for an improved device and method for monitoring the water temperature in a pressurizer vessel which overcomes the deficiencies of the presently known and utilized method and device.